Ape City needs food from Painted Valley, a lush area. The farming down is inhabited solely by Chimps. Zaius' son-in-law, Vitus, is negotiating a deal with the farmers to have the gorillas pick up and transport the vegetables back to Ape City, which is in tatters after the moon/flood disaster. However, Milo holds up a mutated tomato and says their crops are worthless. The only water source flows out of the cave
Meanwhile, In Ape City, there's a Chimp refugee camp that' being run by the gorillas and they are forcing the healthy apes to work. One of the soldiers pulls out young Lucius from the food line and his Aunt Zira tries to stop in. In comes Prisca, who says Lucius is working for her. After she takes the two back to her tent Zira expresses her interest in studying humans and then asks if she's heard anything about Cornelius.
Back in Painted Valley, Dr Milo and Cornelius go to investigate the source of the water that feeds into the valley. A huge, wolf/ape monster appears--but Milo suspects it's just an illusion. Rather than be frightened, he walks right through the mirage. They come to the underground river--and a rowboat. There's another illusion, of a huge wave, but it's another illusion. When they see lights further into the massive cavern they are stopped by a horrible sound and grip their heads in pain. Then, we see the inhabitants--they are mutant chimpanzees who look just like the mutant humans that live beneath the Forbidden Zone...
This series continues to set up a fascinating back-story to the original Apes movies and I thought it very cool there's mutant apes, a nod to the Marvel POTA magazine run in the 70's.